1. Field of the Invention
This invention generally relates to an apparatus for reducing upshift shock in a vehicle with an automatic transmission. More specifically, the present invention relates to an apparatus for reducing upshift shock caused by torque retraction that occurs during a torque phase of an upshift operation of an automatic transmission.
2. Background Information
Generally, an automatic transmission has a plurality of frictional elements such as clutches or brakes, which are selectively hydraulically operated to establish a plurality of speed ratios or gear positions within a multi-ratio automatic transmission. More specifically, the transmission can be shifted to different gears by changing the frictional elements that are engaged.
When the automatic transmission shifts from a lower gear to a higher gear (hereinafter referred to as upshift), a torque retraction phenomenon usually occurs. During the torque retraction phenomenon, which occurs as the transmission is upshifted, an output torque first decreases sharply, and then increases sharply before the output torque is eventually adjusted from the initial torque before the upshift operation to the new torque after the upshift operation. The phase in which the output torque decreases sharply is called a torque phase, while the phase in which the output torque increases sharply and eventually becomes adjusted to the new torque after the upshift operation is called an inertia phase. In particular, an effective gear ratio, which is the ratio of the input rotation to the output rotation of the transmission, changes during the inertia phase.
During the torque phase, which occurs immediately preceding the inertia phase, the output torque decreases sharply, as described above. Accordingly, this torque retraction phenomenon causes an upshift shock accompanied by a sensation of vehicle deceleration. Since this torque retraction phenomenon is well known in the art, details of the torque retraction phenomenon, the torque phase and the inertial phase would be obvious to one of ordinary skill in the art without further explanation herein.
As indicated in Laid-Open Japanese Patent Publication No. 3-129165, the upshift shock due to the torque retraction phenomenon has been conventionally mitigated by temporarily increasing the input torque from the power source (hereinafter called torque up operation) during the torque phase of the upshift operation of the automatic transmission, thereby canceling out the reduction in torque due to the torque retraction phenomenon. After this torque up operation, the input torque of the power source is decreased (hereinafter called torque down operation), in order to cancel out the sharp increase in torque during the inertial phase.
The torque down operation has to be conducted before the inertia phase of the torque retraction phenomenon starts. However, with such conventional methods, there is no guarantee that the aforementioned torque down operation will start before the inertia phase starts. Specifically, the inertia phase starts at different timings depending on the load conditions of the power source and the gear upshift selection, i.e., which gear the transmission is being upshifted to. Therefore, there is always a risk that the torque down operation will not be initiated until after the inertia phase has already started.
If the torque down operation is conducted after the inertia phase has already begun, this means that the inertia phase starts while the torque up operation is still in effect. In other words, at the beginning of the torque phase, the input torque from the power source has been increased to cancel out the effect of the torque reduction from the torque retraction phenomenon. Accordingly, the input torque has not been decreased at the beginning of the inertia phase. Consequently, it will not be possible to prevent the occurrence of an upshift shock that occurs at the beginning of the inertia phase. Furthermore, depending on the size of the torque, it is also possible that the inertia phase may not even start until the torque down operation is completed.
In view of the above, there exists a need for an upshift shock reducing apparatus which overcomes the above mentioned problems in the prior art. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
The object of the present invention is to provide an upshift shock reduction apparatus that consistently starts the torque down operation before the inertia phase starts to ensure reduction of shock during the upshift operation.
The aforementioned object can be attained by providing an upshift shock reducing apparatus for a vehicle having a power train that includes a power source and an automatic transmission having a plurality of shift gears. The upshift shock reducing apparatus comprises a power source sensor that produces a signal indicative of a power source load of the power source, and a controller operatively coupled to the power source sensor, the power source, and the automatic transmission. The controller is configured to increase torque of the power source during a torque phase of an upshift operation for a first predetermined period, and decrease the torque of the power source by a first predetermined torque at an end of a second predetermined period. The second predetermined period is determined based on the signal from the power source sensor, such that the decrease of the torque starts before an inertia phase of the upshift operation.
These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses preferred embodiments of the present invention.